The pump of the present invention is especially useful for operating a movable ram of a press of the general type illustrated in U.S. Pat. No. 3,283,699. A pump of the two-stage hydraulic type with which the present invention is concerned is illustrated in U.S. Pat. No. 2,948,222 and is designated as being especially useful in connection with hydraulic jacks. The pump of the latter patent is difficult to construct and maintain in that the piston is ported and carries a check valve. It is also necessary to construct a cavity for receiving an unloading valve as well as other check valves for operating the two-stage system.
Accordingly, it is an important object of the present invention to provide a two-stage pump structure wherein the check valves and duct means may be confined to the housing permitting a simple cylinder arrangement having two diameters without internal valving.
It is a further object of the invention to provide a simple valving system for a two-stage pump having a manually operated piston of two diameters.